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The Search for the Perfect Antenna . . .

Discussion in 'Amateur Radio Antennas' started by Riverman71, Dec 5, 2018.

  1. w9cll

    w9cll W9WDX Amateur Radio Club Member

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    Yes it will work just fine. If you're going to build it why not make a fan dipole, just make different wires for each band.


     

  2. 543_Dallas

    543_Dallas Sr. Member

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    You could make a fan dipole or take the g5rv approach if you want to experiment. Find a length of antenna and feedline that gives you a reasonable swr on a few bands. Start with the measurements for a g5rv jr and go from there.

    You could also use a trapped dipole.
     
    Riverman71 likes this.
  3. Riverman71

    Riverman71 Part-time Member

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    Looking into that as well. (y)
     
  4. Riverman71

    Riverman71 Part-time Member

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    Handy Andy likes this.
  5. Riverman71

    Riverman71 Part-time Member

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    Oh, oh. Got a latecomer to the contest.

    It's a hamstick dipole. It's a fan dipole. It's BOTH! It's MFJ's new OCTOPUS!

    https://www.hamradio.com/detail.cfm?pid=H0-016465



    Rather than 10/20/40/75 meters as Eric uses in the video, I'm thinking 6/10/15/20 for improved efficiency.

    Havin' fun now!
     
  6. StrangeBrew

    StrangeBrew Sr. Member

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    I seem to remember a set of crossed dipoles that was supposed to give dipole performance but in an omnidirectional pattern, I believe it was called a "turnstile". I wonder if this could be set up as a two band turnstile eliminating the need to rotate it.
     
    Shadetree Mechanic likes this.
  7. Riverman71

    Riverman71 Part-time Member

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    The Octopus is cool, but as a permanent base antenna the Cobweb wins the arm-wrestling contest between the two for these reasons:

    a. More efficient (full length wire dipoles versus shortened hamsticks)
    b. Smaller footprint (9' square vs 14' square)
    c. Cheaper ($229 versus $260 (Cost of Octopus base + eight MFJ hamsticks)
     
  8. Riverman71

    Riverman71 Part-time Member

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    Not sure. Everything I've read about the Octopus says each pair of hamsticks is somewhat directional like any horizontal dipole. Especially the higher it's mounted.
     
  9. StrangeBrew

    StrangeBrew Sr. Member

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    On a turnstile its basically two dipoles in a cross, off the end of one dipole is broadside to the other. So it would take two pair of identical hamsticks to make one array. Of course this would mean you could only set it up for half as many bands.

    I did a bit of googling after my last post though and did find a problem, the two dipoles that make up the system aren't fed in phase so I don't think the connections in that thing would work. Of course you could probably work that out but at that point the thing becomes nothing more than an expensive mount.

    So just forget I said anything.:oops:
     
    #39 StrangeBrew, Dec 13, 2018
    Last edited: Dec 13, 2018
  10. Riverman71

    Riverman71 Part-time Member

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    Oh, I misunderstood what you were saying. Now I get it.
    One pair covers east/west and the other north/south. (y)
    Never heard of the turnstile dipole.
     
  11. Riverman71

    Riverman71 Part-time Member

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    MFJ's selling points for the cobweb are: "Omni-directional. No radials needed! Works great at low heights."

    Is the low heights claim hogwash? Regular horizontal dipoles need height to improve take-off angle, among other things. Does the shape of the cobweb's dipoles affect how they perform at low heights? Anyone?
     
  12. 543_Dallas

    543_Dallas Sr. Member

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    You can always find someone that will tell you an antenna works great but I'm not knocking the cobweb if it fits your needs. Low height will hurt it just like it does a dipole because the lower it is the more ground loss you have. I would rather have a dipole or doublet which are also omni directional when low to the ground relative to the frequency you're using. It may be a decent antenna but I think there's some creative advertising there.
     
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  13. binrat

    binrat WDX Club Coordinator
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    543 has a point. An antenna's height matters for the most part. I have found verticals are less effected by lack of height.
     
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  14. Riverman71

    Riverman71 Part-time Member

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    Had a idea about the cobweb. What if small "L" bracket is added to the top of the mast and the antenna is mounted vertically? I believe one benefit of vertical dipoles over horizontal ones is a lower take-off angle. Don't know if this would apply to the cobweb given the shape of its dipoles.

    Guess you could do this with the Octopus as well. Vertically, it would have one vertical dipole, two slopers and one horizontal.
     
  15. Riverman71

    Riverman71 Part-time Member

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    Just ordered the MFJ-1836 Cobweb. (y)
     
    Tallman, PA770 and Shadetree Mechanic like this.

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